We have shown that food deprivation of preweanling and adult rats causes marked changes in liver responsivity to adrenergic agonists. While short-term food deprivation of preweanling rats decreases liver ODC induction by both alpha and beta agonists, food deprivation of adult rats increases responsivity to beta agonists and decreases responses to alpha agonists. The changes in responsivity are accompanied by changes in receptor number in adults but not neonates. The goal of this proposal is to investigate the altered responsivity to alpha and beta adrenergic agonists which result from food deprivation of neonatal and adult rats, with a particular emphasis on investigating the opposite responses of neonates and adults. The role of altered receptor number and/or coupling in the altered liver ODC response will be studied. Alpha1, alpha2 and beta receptors in liver and heart will be quantitated, and compared to liver and heart ODC induction by the specific agonists phenylephrine and isoproterenol after different durations of food deprivation in preweanling and adult rats. In addition, the effect okf food deprivation on other indices of end organ responsivity to adrenergic agonists including glycogen phosphorylase will be investigated both in vivo and in vitro. Finally, the role of specific nutrients in the altered responsivity which occurs during food deprivation will be assessed in specific refeeding experiments, and preliminary studies of potential physiological mediators of the response (catecholamines, glucose, etc.) will be conducted. An additional goal of these studies is to investigate the hypothesis that the contribution of alpha and beta mechanisms to sympathetic regulation in liver changes during development, and to determine if these changes are related to hepatic responses to food deprivation. These studies should provide considerable insight into the fascinating possibility that nutritional status is an important regulator of end organ responsivity to sympathetic agonists in developing and adult animals. In addition, these studies should provide valuable information about peripheral adrenergic receptor regulation in maturing animals, which our preliminary data suggests differs considerably from regulation in adult animals.